Cell Cycle and Chromosomes

Early in the history of biology, scientists believed cells arose spontaneously. With the development of cell theory, people finally realized that only cells can beget other cells. In fact, two categories that define something as living or not are growth and reproduction, both of which cell division accomplishes. Cell division, also called mitosis, occurs in all living things. As living things grow, some cells die or become damaged and need replacements. Some single-celled organisms use a type of mitosis as their only form of reproduction. In multicellular organisms, cell division allows individuals to grow and change by expanding the number of total cells. The division of the nucleus is equal during cell division. This ensures the characteristic of both parent cell in daughter cells and restores the size of the nucleus.

Mitosis is equational division and meiosis is reductional division. Both consists of 4 phases, namely prophase, metaphase, anaphase and telophase. Prophase is the first phase of both mitosis and meiosis I. During this phase, the chromatin condenses and forms visible chromosomes. The mitotic spindle begins to form, nucleolus disappears, the nuclear envelope disappears. 

1. In G$ _1$  phase the amount of DNA is the same as 40 because the cell is metabolically active but no division of DNA is observed.
   
2. In G$ _2$ phase the DNA gets doubled as it has gone through the synthesis phase which is characterized by the replication of DNA.
3. In mitosis since equational division occurs the DNA content remain 4C through the process before the transfer of DNA into daughter cells.

G$ _1$ , S , G$ _2$, M , cytokinesis. The correct sequence has G$ _1$ as a preparation for S and G$ _2$ as the time between the completion of S and entry into M. Cytokinesis occurs after the other stages to create two daughter cells.

The cell cycle mainly consists of 4 stages G$ _1$, S, G$ _2$, and M. The G$ _{0}$ phase also known as the extended G1 phase is a period in which the cell exits from the cell cycle. In this stage, the cell exists in a quiescent state and does not divide. Thus the correct answer is option A.

During the cell cycle, RNA and protein synthesis takes place during G$ _1$ and G$ _2$ phase. The cell cycle is an ordered set of events, culminating in cell growth and division into two daughter cells. Non-dividing cells not considered to be in the cell cycle. The stages are G$ _1$-S-G$ _2$-M.

G1 phase and the other subphases of the cell cycle may be affected by limiting growth factors such as nutrient supply, temperature, and room for growth. Sufficient nucleotides  and amino acids must be present in order to synthesize mRNA and proteins. Physiological temperatures are optimal for cell growth. In humans, the normal physiological temperature is around 37 C. Therefore, the correct answer is option D.

Generation time is defined as the total time taken by a cell to complete one full cell cycle, which includes interphase and the M-phase.

The eukaryotic cell cycle follows a specific sequence: G1 phase, followed by the S phase (DNA synthesis), then the G2 phase, and finally the M phase (mitosis), which concludes with cytokinesis.

The cell cycle includes a series of events, that take place  in a cell which leads to the duplication of DNA and division of cells to form two daughter cells. This takes place in three different  periods and can be referred to as Interphase , Mitotic phase(M) and cytokinesis. While during the interphase or the initial phase, the cells grow in size and is ready for division, during the mitosis, the DNA starts duplicating, the nuclear membrane dissolves and the cells starts its division process to give rise to  two distinct daughter cells. Cytokinesis is the stage during which the two daughter cells are formed and separated.
So, the correct answer is option D.

One cell cycle of yeast is almost 90 minutes and a human cell takes almost 24 hours to divide by mitosis therefore by calculations it seems that a yeast can perform mitosis almost 16 times in the time of 1 division of a human cell.

Through phosphorylation, Cdks signal the cell that it is ready to pass into the next stage of the cell cycle. As their name suggests, Cyclin-Dependent ProteinKinases are dependent on cyclins, another class of regulatory proteins. Cyclins bind to Cdks, activating the Cdks to phosphorylate other molecules.

So, the correct option is ‘binding to cyclin, plus, phosphorylation by Cdk activating protein kinases’.